A federal court in Louisiana has dealt a serious blow to the Biden administration’s effort to protect communities heavily affected by toxic industrial pollution.

The U.S. District Court for the Western District of Louisiana ruled on Wednesday that the Environmental Protection Agency is barred from using the federal civil rights law to prevent Louisiana from granting permits for numerous polluting facilities in minority and low-income communities.

Title VI of the 1964 Civil Rights Act allows the E.P.A. to investigate whether state programs that receive federal money are discriminating on the basis of race, color or national origin.

But the judge’s ruling effectively means that the federal government is limited to taking action against specific agency decisions that are intentionally discriminatory. The E.P.A. cannot, however, consider cumulative or “disparate” environmental harms. That means the state cannot be held liable for actions like allowing several chemical plants, refineries and other industrial operations in minority communities.

Debbie Chizewer, an attorney at Earthjustice, an environmental group that has pursued Civil Rights Act cases on behalf of heavily polluted communities, called the decision “outrageous.” She said: “Residents were already struggling because of the disproportionate exposure to environmental harms in Louisiana. This leaves them unprotected.”

The E.P.A. issued a statement saying the agency and the Justice Department “remain committed to enforcing civil rights law, consistent with the court’s order” and said in the coming weeks the agency would determine its “next steps to ensure nondiscrimination in the programs and activities our agencies fund.”

The ruling applies only to Louisiana, though environmental activists said the case could have national implications if other states opened legal challenges similar to Louisiana’s.

In April, Republican attorneys general from 23 states petitioned the E.P.A. to stop taking race into account when regulating pollution, underscoring opposition in Republican states to the Biden administration’s agenda. The administration has made environmental justice, or addressing the unequal burden that low-income and minority communities face from environmental hazards, a top priority.

The case stems from a 2022 E.P.A. investigation into whether Louisiana had violated civil rights laws by permitting scores of industrial facilities to operate in and around St. John the Baptist Parish, a predominantly Black community.

Residents in the area had been calling for change for decades and the investigation marked the first time the federal government appeared to be taking sweeping action there.

The E.P.A. and the Louisiana Department of Environmental Quality spent months negotiating an agreement that would have changed Louisiana’s air pollution permitting program, making it harder to disproportionately effect certain communities with toxic pollutants.

But then in May of 2023, the attorney general of Louisiana sued the E.P.A. and the negotiations stopped. The E.P.A. closed its investigation, but Louisiana pursued its legal challenge.

The judge in the case, James D. Cain Jr., also declined a request from the federal government to dismiss the case, ruling that Louisiana had a right to “unambiguous clarity concerning Defendants’ power to regulate beyond the plain text of Title VI.”

In January, Judge Cain offered a preliminary ruling in favor of the state that foreshadowed Wednesday’s decision.

The Biden administration has sought ways to work around the courts on curbing environmental hazards in communities that surround industrial sites, primarily by enforcing aggressive new regulations.

In April, for example, the E.P.A. issued new a new rule requiring more than 200 chemical plants across the country to reduce the toxic pollutants they release into the air. It was the first time in nearly two decades that the government had tightened limits on pollution from chemical plants, and it came after Michael S. Regan, the administrator of the E.P.A., traveled to St. John the Baptist Parish.

“I saw firsthand how the multigenerational and widespread effects of pollution were affecting the health of the local community,” Mr. Regan said.

Most of the facilities affected by the rule are in Texas, Louisiana and elsewhere along the Gulf Coast as well as in the Ohio River Valley and West Virginia. Communities in proximity to the plants are often disproportionately Black or Latino and have elevated rates of cancer, respiratory problems and premature deaths.

The rule specifically targets ethylene oxide, which is used to sterilize medical devices, and chloroprene, which is used to make rubber in footwear.